1. Field of the Invention
This invention relates to a bidirectional line switched ring network control system for bidirectionally transmitting signals by connecting a plurality of nodes in a ring form.
Introduction of a bidirectional line switched ring network BLSR utilizing a synchronous optical network SONET is expected. When any trouble or failure occurs in such a bidirectional line switched ring, processing must be rapidly sped up.
2. Description of the Related Art
When no trouble exists in the ring network, each of the nodes in the bidirection line switched ring network receive an APS (automatic protection switching) byte of K1 and K2 bytes of an overhead on a multiplexed signal flowing through the ring network, generates afresh a new APS byte for transmission signal and transmits it. At this time, each node adds the address of the next node, and this address is mainly constituted by the K1 byte. It also effects branching and insertion of payload, and changes to a pointer, etc., of the overhead thereby generated. When any trouble occurs in the ring network, nodes on both sides of the position of the occurrence of the trouble form a turn-back circuit for the payload, and the other nodes continue their normal operation. In this instance, message must be exchanged and the turn-back circuit must be formed between the nodes on both sides of the position of the occurrence of the trouble, while the other nodes must transmit the APS byte containing the address for this message exchange.
Normally, each node receives the APS byte. When any trouble occurs as described above, however, each node must pass the APS byte for the message exchange. Conventionally, the transmission processing of this APS byte has been carried out using software. Therefore, as the number of nodes becomes greater, the processing time accumulates and the time for relieving the trouble by forming the turn-back circuit is prolonged.